The invention regards generally displays of the type where an image is created, normally electrically and pixel by pixel, and is brought to a viewable image, preferably a virtual image, which can be combined with a real image, for instance a scene.
A display of this type is known from U.S. Pat. No. 5,596,451, the contents of which are hereby declared as included by reference in the present disclosure. An active matrix liquid crystal matrix of the type marketed by Displaytech, Inc., Boulder, Colo., USA may have a very high number of pixels on a small chip, and the pixels change their polarization of reflected light. Such a matrix is mounted in a glass prism system with an illumination device, which directs polarized light toward the matrix. The light reflected from the matrix will then have its pixels reflect the polarized light with the same or a different polarization state, depending on the pixel being in one or the other of two states of electrical activation, and the image created by the settings of the pixels is projected via polarization means for eliminating radiation having one of the polarization states, toward the eye of an observer, may then be seen as a virtual image at a distance, eventually also together with a natural scene, creating an effect roughly corresponding to that of a HUD (Head Up Display).
In this patent and in U.S. Pat. No. 5,808,800 are shown displays for head mounting of the type comprising an active matrix liquid crystal image generator, an illumination device for illuminating the said image generator and optical means for projecting an image generated by the image generator toward an exit pupil at an eye location for viewing by an eye together with an eventual natural scene in front of the eye emplacement, said optical means comprising prisms forming two mutually parallel beam splitters, each formed by the jointure of two prism surfaces in a beam splitter layer, a first one of said beam splitters reflecting light from said illumination device to illuminate said image generator, a spherical mirror imaging said illuminated image generator by reflecting light from said image generator traversing said first beam splitter and said second beam splitter, said second beam splitter reflecting light reflected by said spherical mirror toward said eye location.
In this known system (U.S. Pat. No. 5,596,451), there are used two cubes (or at least having square sections), both consisting of right isosceles prisms joined at their hypotenuse faces, forming polarizing half-mirror layers in between. A first of the cubes has the matrix laid on one cube side, and its polarizing half-mirror is used for illuminating the matrix. The matrix is imaged through the half-mirror and into the second cube through its half-mirror layer and a .lambda.-quarter layer (converting the light to circular polarization) up to a planoconvex mirror laid flat against the cube. The reflected rays (with opposite circular polarization) will be linear polarized but in a perpendicular direction in relation to the light coming from the first cube, when returning through the .lambda.-quarter layer. The polarizing half-mirror layer in the second cube will therefore direct the light toward the eye. Since the eye can also look through the second cube, the image and the natural scene can be regarded simultaneously. However, the scene can also be removed by a blind or the like, creating also a viewing device usefull e.g. for "virtual reality".
In the examples shown in U.S. Pat. No. 5,596,451, the first cube carrying the display matrix is smaller than the second cube, which is also used for viewing through. Lately, the matrixes have increased in size and number of pixels, so that devices with 1280.times.1024 pixels can now be obtained, the chip having a size of 16.times.13 mm in total. Also, it is advantageous to make the second cube as small as is consistent with demands for eye relief. The general construction could then evolve toward a system as shown in FIG. 1, which is different from the said prior art.